Clofarabine [2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine] has exhibited cytotoxicity in mice inoculated with P388 leukemia. As reported by Montgomery et al., Synthesis and Biologic Activity of 2′-Fluoro-2-Halo Derivatives of 9-β-D-Arabinofuranosyladenine, Journal of Medicinal Chemistry, 1992, 35, pp. 397-401, clofarabine provided a good increase in life span of mice inoculated with P388 leukemia. The 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine was the most effective compound in the tested system. In addition, this compound exhibited reduced cleavage in vivo of the glycosidic bond as compared to Fludarabine.
The reported method for synthesizing 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine comprises a procedure using 3-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-D-arabinofuranosyl bromide for the coupling with 2,6-dichloropurine, followed by an amination/deprotection sequence. (See Montgomery, et al., 9-(2-Deoxy-2-fluoro-β-D-arabinofuranosyl)guanine: A Metabolically Stable Cytotoxic Analogue of 2′-Deoxyguanosine, Journal of Medicinal Chemistry, 1986, 29, pp. 2389-2392; and Montgomery et al., Synthesis and Biologic Activity of 2′-Fluoro-2-halo Derivatives of 9-β-D-Arabinofuranosyladenine, Journal of Medicinal Chemistry, 1992, 35, pp. 397-401).
However, the reported method for synthesizing 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine resulted in low overall yields of product, typically in the range of about 13%. The described coupling reaction produced a mixture of nucleosides from which the desired 9-β intermediate was obtained in only 32% yield after careful chromatography. Direct amination/deprotection of this material gave the desired 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine, plus a partially benzoylated 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine that required further base treatment. Pure 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine was obtained only after several recrystallizations to remove salts and residual benzamide.
Such inefficient reactions will inhibit the ability to commercially produce 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine. Thus, there is a need for an improved method for synthesizing 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purin-6-amine that results in increased yields and/or reduced process steps.